Ask the Experts Q&As are culled from member inquiries to NTCA’s Technical Team. To become a member and make use of personal, targeted answers from NTCA’s Technical Team to your installation questions, contact Jim Olson at [email protected].
QUESTION
I am an architect and have a question about moisture in showers. We designed four showers in an apartment completed in September 2023 that appear to have been built properly as far as we can tell from site observations and speaking to the contractors.
Our client used a pinless moisture meter on the floor of their four showers (PROTIMETER SurveyMaster BLD5365) and found a high moisture level 3/4″ below the finish surface. Beyond the showers the finish floor has a lower moisture level. There is no leakage nor any damage – just this measure of high moisture. I spoke with the thinset mortar manufacturer and they said moisture will not degrade the thinset. The client measured the moisture while measuring an unrelated moisture issue.
My question is whether there is any issue with moisture being detected in a shower pan? I have never had a client measure moisture in this way. Is there any data on acceptable levels of moisture? Could the lead pan trigger the moisture meter to give false readings? Client is concerned mold will grow. Two showers are never used and I have no idea where moisture could be coming from.
ANSWER
It stands to reason that showers have a higher moisture content than the dry area beyond. Our team would expect the moisture amounts to be higher in a packed mud bed as it takes a while for the water to weep through. If the showers that are being used are not properly sloped to drain or if there is a slow draining mud pack or weep holes are beginning to clog, these showers may be retaining more moisture than we would normally expect. If there are no visible leaks and no long-lasting discoloration with the grout or stone or no unusual smells we don’t see a cause for concern. Since it sounds like there are no leaks or any immediate concerns we would assume the showers are functioning properly.
We do not have any knowledge of lead pans affecting moisture content beneath the tile layer unless there is a problem with the slope to drain with the drain being higher than the pitch where slope meets it.
We agree with the thinset manufacturer – the moisture won’t affect the thinset mortar bond coat.
We feel the potential for mold growth is limited but could possibly grow on the top surfaces when fed by soaps or shampoos and organic materials; this could be easily prevented by routine cleaning.
